This invention relates to improvements in control terminals which permit their safe use in hazardous locations. In particular, these improvements permit operation of electronic data terminals in environments containing explosive concentrations of inflammable gases, dusts, or vapors.
Computer control of manufacturing processes can provide increased precision by enabling real-time process adjustment by employing electronic analysis of sampling data and control feedback signals. This requires placement of input/output data terminals and monitors at critical points in the process stream where sampling data are collected and process adjustments made.
Many manufacturing processes, however, involve inflammable volatile solvents or gases, vapors, or dusts which present a danger of fire or explosion. In such environments, electronic data terminals must provide absolute certainty that they cannot cause a fire or explosion by arcing in the presence of the hazardous atmosphere. This assurance is critical in petrochemical plants, munitions plants, welding gas plants, and paint factories as well as in grain elevators and other operations which produce inflammable dust.
One common approach to avoidance of the explosion hazard in such facilities has been to locate all controls remote from the hazardous environment. This configuration requires communication between the remote data terminals and the process adjustment points which adds oportunities for delay and error.
In order to provide this safety while retaining the localized control it is desirable to provide atmospherically isolated regions for connection of primary power sources, electronics for control of purge timing and for purge maintenance, and electronics for terminal operation.
An object of this invention, therefore, is to provide a control terminal which is safe for use in explosive or inflammable environments by preventing the explosive atmosphere from contacting any potential arc source.
Besides the explosion hazard, many facilities have environments which can damage or destroy electronic equipment due to the effects of ambient atmosphere.
A further object of this invention is to provide a control terminal which is shielded from the deleterious effects of dirt, corrosive vapors, humidity, excessive ambient temperatures, and combinations of these hazards.
The terminals of the present invention provide the necessary safety and atmospheric shielding, and, since they can be placed in the hazardous environment at the process control points, eliminate the delay and error potential associated with remote location. Using these terminals, the operator at each location can monitor the process and immediately make adjustments as required.
The objects of the invention and the means for accomplishing said objects will be readily understood by reference to the drawing and the descriptions thereof which will enable one skilled in the art to make and use the invention.